Method of and Device for Safeguarding Operation of an Internal Combustion Engine

The present invention relates to a method of safeguarding operation of an internal combustion engine, particularly of a Diesel engine having a fuel tank, a fuel metering device, an electrically controlled fuel pump for supplying fuel from the tank to the metering device, means for injecting fuel into cylinders of the engine in response to momentary operational conditions of the engine.

To supply fuel from a tank to fuel metering systems of an internal combustion engine via electrically controlled fuel pumps is known from prior art. The metering systems can include carburators of an arbitrary shape and design or arbitrary fuel injection devices. In the case of self-igniting internal combustion engines (Diesel engines) there are usually provided mechanically driven fuel injection pumps whose delivery of fuel to be injected is determined by a hydraulic or magnetic control mechanism. Even in the latter case fuel is supplied to a high pressure fuel injection pump via a low pressure electrically controlled fuel supply pump. Especially in the case of Diesel engines the safety considerations must be taken into account because a control rod which determines the delivered fuel quantity in series connected fuel injection pumps may become accidentally clamped for example due to the intrusion of a foreign particle or due to the effect of other interferences and an emergency situation in the engine operation may occur.

It is, therefore, a general object of the present invention to safeguard the operation of the engine even in the case of such emergency situations.

In particular it is an object of this invention, especially in the case of Diesel engines, to adjust the supply of fuel to the fuel metering system in such a manner as to guarantee normal operation on the one hand, and in emergency situations or in the case of a malfunction to immediately react for example by stopping the engine, on the other hand.

In keeping with these objects and others which will become apparent hereafter, the method of this invention includes the steps of providing an additional electrically controlled fuel pump for supplying fuel from the tank to the metering device, during starting operation when rotary speed of the engine has a low value n being less than an idling speed, activating both fuel supply pumps, during a normal engine operation when rotary speed n is larger than the idling speed, activating at random only one of the two fuel pumps to supply to the metering device in approximately equally distributed running times of the two pumps, and in an emergency situation when an actual rotary speed exceeds a predetermined speed limit for a predetermined time interval, activating both fuel pumps in reverse run to suck fuel from the metering device.

The invention has the advantage that in normal engine operation a considerable safety redunancy results from the provision of two randomly activated fuel supply pumps. Due to the monitoring of operational conditions of the engine, namely the rotary speed, the difference between the actual and nominal values of the gas pedal position and in the case of a Diesel engine, the actual and nominal positions of a control rod which determines the quantity of injected fuel, or the nominal and actual values of load in all types of engines and the processing of the latter either in separate evaluation and control devices for the fuel supply pumps or in connection with existing computers or microprocessors, it is guaranteed that in operational conditions leading to emergency situations the two fuel supply pumps are operated in reverse running so as to immediately bring the engine to a standstill.

It is also of advantage that actuation or running times of the two fuel supply pumps are substantially equally distributed because in spite of slightly increased expenditures due to the doubled actuation, in the end effect the increased expenditures are compensated for in emergency situations when due to the reversal of running of the two fuel supply pumps a substantially faster removal of fuel present in the fuel metering system or in the fuel injection pump of a Diesel engine, a faster stoppage of the engine is achieved.

The device of this invention includes a controlling device for the two fuel supply pumps which can be with advantage designed in such a manner to monitor the operational conditions of the two pumps and in the event of a defect detected in one of said pumps, to automatically switch over the operation to the remaining pump. A defective pump operation can be recognized for example from the comparison of a stored nominal value of the regulating or control mechanism with the actual value thereof then the two fuel supply pumps are switched on for forward delivery.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

The single FIGURE illustrates a flow chart of different modes of actuation of the two fuel supply pumps in response to different operational conditions of the engine.

This invention is based on the provision of two parallel operating electrically controlled fuel supply pumps EKP1 and EKP2 for delivering fuel to a metering or injection device of an internal combustion engine and to control via a central controlling device the actuation of respective fuel supply pumps in response to operational conditions of the engine.

The following description of an example of this invention is concerned with the operation of a Diesel engine having an electronic fuel injection control (EVC) which applies the requisite control signals to a control mechanism for the operation of a fuel injection pump EP. It will be noted however that this invention is not limited to this specific exemplary embodiment but can be used for other types of internal combustion engines. Moreover, the control unit or device generating particular control signals for the operation of respective fuel supply pumps EKP1 and EKP2 according to various operational conditions of the engine can be realized either by hardware or completely or partially by a program in a supervisory central control device (a computer or microprocessor) controlling the overall operation of the engine or of the motor vehicle.

In the present example, as mentioned before, the two electrically controlled fuel supply pumps EKP1 and EKP2 supply fuel to a non-illustrated fuel injection pump EP regulated by an electronic Diesel engine controlling device EVC.

Referring now to the drawing, the actuation of respective fuel supply pumps EKP1 and EKP2 is controlled in response to different operational engine conditions as follows:

1. After turning on ignition during starting operation

a control device for the two fuel pumps activates both pumps EKP1 and EKP2 to deliver fuel simultaneously as indicated in block I;

2. If during the starting operation the control device detects that

a. the rotary speed of the engine approaches zero (n less than 10 rpm) and simultaneously

b. the gas pedal position FFG remains zero (LL) for a predetermined time interval .DELTA.T then both pumps EKP1 and EKP2 are turned off as indicated in block II.

3. If during the condition of turned off pumps the actual rotary speed exceeds a predetermined minimum value (n greater than 10 rpm) or if the gas pedal position becomes greater than zero then both fuel supply pumps EKP1 and EKP2 are reactivated (block I).

4. If during the staring condition corresponding to the block I (both fuel supply delivering) the rotary speed of the engine exceeds idling speed (n greater or equal to n.sub.LL) then a random one of the two active fuel supply pumps is turned off and only the other fuel supply pump continues the delivery so that then the engine is in its normal mode of operation (block III).

5. If during this normal operation the control device detects drop of rotary speed below the predetermined minimum value (n less than 10 rpm) then the turned off fuel supply pump is reactivated and the operation of both pumps EKP1 and EKP2 is controlled again according to the blocks I and II pertaining to the staring condition of the engine.

6. During the normal engine operation the control device monitors for malfunction or an emergency engine operation. Such an abnormal condition is detected for example when the difference between the actual and the nominal value of the regulating signal of the control rod is greater than a predetermined limit stored in a computer memory and the transgression of the regulating difference lasts longer than a stored time limit interval .DELTA.T.sub.lim. In this event a fault or an emergency operation has been detected. Such a transgression of the regulating difference resulting as explained above from the condition that the actual regulating value is less than a desired or nominal regulating value whereby the difference between the regulating difference and a limit value when applied to the position of control rod, can be expressed in length units for example in millimeters (RW actual less than IW nominal by one millimeter). In this defect condition which occurs also during malfunction of the active pump, both fuel supply pumps EKP1 and EKP2 are switched on for delivery as indicated in Block IV. This defect condition is not established when

a. the preceding conditions are detected while the difference between actual and nominal regulating values is positive, that means when the nominal value is smaller than the actual value (emergency situation);

b. when the preceding condition was an emergency situation (which will be explained below in connection with block V) and a predetermined stored time interval .DELTA.T.sub.look had not yet expired.

7a. The above mentioned condition 6a (nominal regulating value is less than the actual value) represents an emergency situation when the difference exceeds a predetermined limit and simultaneously the actual rotary speed exceeds a predetermined value for a predetermined time limit interval. By way of an example, the emergency situation will occur when RW actual is greater than RW nominal plus 1 millimeter and rotary speed is greater than 1000 rpm, both conditions lasting more than a predetermined time interval .DELTA.T.sub.lim =200 milliseconds.

b. The emergency operational condition results also upon the detection of overspeed, that means when the actual rotary speed exceeds a predetermined speed limit value for a predetermined limit time interval, for example when rotary speed is greater than 2,700 rpm over .DELTA.T.sub.lim of 20 milliseconds.

Upon the detection of an emergency situation during the engine mode of operation correspondings to blocks III and IV, both fuel supply pumps EKP1 and EKP2 are switched over into reverse run so that they suck out fuel from suction space of a fuel injection pump EV, as indicated in block V. The switchover into reverse can be effected for example by the reversal of polarity of electrical terminals of the two pumps.

8. From the emergency mode of operation the reverse delivery of the pumps can be returned to their normal forward delivery according to block III under the condition that the actual regulating value RW.sub.ist is smaller or equal to the nominal regulating value RW.sub.soll and the actual rotary speed of the engine is smaller than a predetermined lower speed limit value, for example n is less than 2,600 rpm.

9. From the emergency (suction) mode of operation illustrated in block V the two fuel supply pumps EKP1 and EKP2 can be brought into the turned off condition illustrated in block II provided that after the completion of the suction and upon expiration of a predetermined time interval the rotary speed drops to zero or below a predetermined minimum value (n less than 10 rpm).

It is evident that due to the solution of the control of a pair of electrically controlled fuel supply pumps in accordance with this invention it is guaranteed that at a standstill condition of the engine or when its rotary speed drops below 10 rpm the two fuel supply pumps are turned off. Nevertheless, upon depression of the gas pedal from its idling or zero position (sfg is greater than LL) the two pumps are immediately reactivated (transition from block II to block I); in the case of a Diesel engine having a fuel injection pump EP controlled by a control rod of a Diesel engine control unit, the control rod is brought into its nominal position upon actuation of the starter thus improving the cold start. During the normal operation of the engine, when only one of the two fuel supply pumps is turned on, and a defect develops in the active pump the control device immediately switches over to the second fuel supply pump. The switchover is effected in such a manner that upon the recognition of a defect when the actual control value is smaller than the desired control value during the operation of the pumps indicated in block III, both pumps are turned on their normal forward fuel delivery as indicated in block IV.

While the invention has been illustrated and described as embodied in a Diesel engine, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.